1. Field of the Invention
The present invention relates to a piston ring (including a side rail of a combined oil ring) used for internal combustion engines and compressors, and particularly to a piston ring which is effective for internal combustion engines of high speed and high output and a method for manufacturing the same.
2. Description of the Related Art
An implementation of high speed and high output and low friction is intended for recent gasoline engines for automobiles, and the demands of function and quality of piston rings increase accordingly. Thus, it is urgent to solve a problem in that an amount of blow-by abruptly increases when a rotational speed of the engine exceeds a certain limit.
The phenomenon of the abrupt increase of the blow-by is closely related to fluttering of a piston ring. To address this problem, it has been considered to reduce a dimension of a ring width in order to reduce an inertia force of the piston ring or to design a torsion of a top ring.
However, the reduction in the ring width gives rise to the problem of lowering of a rigidity of the piston ring.
On the other hand, as a surface treatment of a piston ring made of steel, attention has been paid to a physical vapor deposition showing wear resistance and scuffing resistance in excess of chrome plating (Japanese Patent Laid-Open Publication Nos. 57-57868, 57-65837, 58-35648, etc.)